雙接面非晶矽薄膜太陽能電池之穿隧複合接面研究

Abstract

在此論文中，薄膜太陽能電池是由27.12 MHz的電漿輔助化學氣相沉積系統所製作，氫化非晶矽雙接面太陽能電池相較於微晶矽與矽鍺合金有材料成本較低的優勢，此外，與在相同厚度的單接面非晶矽太陽能電池有較高的穩定度。這也是一個好的結構去研究穿隧複合接面，利用不同的材料和結構做為穿隧複合接面幫助載子傳輸與複合進而提高電池的效率。首先，非晶氧化矽當作穿隧複合接面可提供缺陷能階提高載子複合，然而，該層的導電性不足幫助載子傳輸與複合，氧化鋅可提高載子複合但並不適合用於底部電流限制的電池，這是由於氧化鋅會將部分的光反射造成底部吸收減少，使得電流不匹配。有參雜的微晶矽作為穿隧複合接面則著重在它的結晶率，然而，為了使其結晶而沉積了過厚的膜會造成過多的吸光，該層必須要足夠薄且有更高的結晶率，藉由提高氫流量比率使該層更易結晶進而減少厚度。最後在這篇論文中，在改進有參雜的微晶矽作為穿隧複合接面後，其電池的開路電壓、短路電流密度、填充系數、轉換效率被提升至1.76 V、7.06 mA/cm2、71.86 %及8.93 %。

In this thesis, the thin-film solar cells were prepared by a radio-frequency (27.12 MHz) plasma enhanced chemical vapor deposition (PECVD) system. The a-Si:H / a-Si:H tandem solar cells have the advantage of a lower production cost, as compared to a-Si:H / a-SiGe:H and a-Si:H / μc-Si:H tandem solar cells. Fouremore, The a-Si:H / a-Si:H tandem solar cell was more stable than a-Si:H single-junction solar cell with the same absorber thickness. It is also a good structure for studying the tunneling recombination junction (TRJ). Various materials and structures were applied as TRJ to assist carrier recombination, as well as improving the performance of cells. First, an amorphous silicon oxide layer was introduced as TRJ to enhance recombination; however, its conductivity was not sufficient to assist carrier transport. The sputtered zinc oxide layer was good for recombination, but it was not suited for the bottom current limited tandem solar cells due to the reflection which reduced the absorption in the bottom cell. The crystallinity of the hydrogenate microcrystalline (c-Si:H) doped layer as TRJ was the critical factor which affected the cell performance. However, the thick microcrystalline doped layers would absorb light which reduced the cell performance. The TRJ was optimized to be thinner and more crystallized. The current limiting cell shifted from the bottom cell to the top cell by decreasing the thickness of microcrystalline doped layers while maintaining its crystallinity with by increasing hydrogen dilution ratio. Finally, the Voc, Jsc, F.F. and η could be improved to 1.76 V, 7.06 mA/cm2, 71.86 % and 8.93 %, respectively, by the optimized microcrystalline doped layer as TRJ in this thesis.